1. Field of the Invention
This invention relates to radar antenna subsystems designed in ferrite type dielectric waveguide transmission line for millimeter wave frequency applications and more particularly to an integrated ferrite circulator/antenna device which functions as both a circulator and an antenna for such millimeter wave frequency applications.
2. Description of the Prior Art
U.S. Pat. No. 4,415,871, issued Nov. 15, 1983 to Richard A. Stern and Richard W. Babbitt, the inventors of the present application, and assigned to the assignee of the present application, describes a ferrite type of circulator device which may be used in millimeter wave frequency applications designed in dielectric waveguide, such as radar system front ends, for example. The circulator device essentially comprises a ferrite right prism having polygonal shaped bases and at least three prism faces which are of equal size and shape. When a dc magnetic field is applied between the bases of the ferrite prism, a non-reciprocal coupling action between the prism faces or "circulator ports" results. The non-reciprocal coupling action is such that an input signal applied to a first port is coupled to a second adjacent port but is effectively isolated from the third port. Similarly, a signal applied to the second port is coupled to the third port but is effectively isolated from the first port. As explained in said U.S. Pat. No. 4,415,871, circulators of this type may be used to couple the transmitter and the receiver of a radar system to the radar antenna by utilizing lengths of dielectric waveguide between the circulator ports and the transmitter, receiver and antenna apparatus.
U.S. Pat. No. 4,424,517, issued Jan. 3, 1984 to the said Richard A. Stern and Richard W. Babbitt and assigned to the assignee of the present application, shows an integrated dielectric waveguide radar front end device utilizing a ferrite circulator having the circulator ports coupled to the radar transmitter and radar receiver by lengths of non-ferrite, dielectric waveguide. The radar antenna also consists of a section of non-ferrite, dielectric waveguide having a series of perturbations extending along one of the sides of the section which radiate the radar signal. The antenna itself is coupled directly to the antenna port of the circulator since the dielectric waveguide materials selected for the antenna section and the input and output waveguide sections of the circulator are fabricated of a low loss dielectric material having a dielectric constant which is closely matched to the dielectric constant of the ferrite circulator material.
U.S. patent application Ser. No. 640,183, filed Jul. 2, 1984 by the said Richard A. Stern and Richard W. Babbitt and assigned to the assignee of the present application, now U.S. Pat. No. 4,691,208, discloses a radar scanning antenna comprising a ferrite rod having a series of perturbations extending along a side of the rod which radiate a radar beam when the ends of the rod are coupled between a source of the radar signal and a load. The radiated antenna beam is swept by means of a pair of thin metallic plates which extend along oppositely-disposed sides of the rod and a helically wound biasing coil which surrounds the metallic plates and extends along the rod.
When the radar system front end utilizes a ferrite type circulator device and a ferrite type scanning antenna, these two components are coupled together by a length of dielectric waveguide material which is selected to have a dielectric constant closely matched to that of the ferrite material of the circulator and the antenna to minimize impedance discontinuities and losses. For proper operation, it is important that the magnetic biasing fields of the ferrite circulator device and the ferrite scanning antenna do not interfere or react with each other. In addition, for many millimeter wave applications, such as for target acquisition systems, for example, it is of critical importance that the radar front end portion of the system be of small size and low weight to facilitate mounting in missiles and guided vehicles.